1. Field of the Invention
This invention relates to a method and apparatus for forming optical elements and more particularly to a method for forming from a mold, optical elements having an optical coating and a tinted hard coat layer.
2. Previous Art
Optical elements having optical coatings are useful in a number of ways. For example, eyeglasses in which the ophthalmic lenses have been provided with optical coatings have several advantages. If the optical coating is a dielectric stack, or a multilayer anti-reflective coating, then eyestrain to the wearer can be reduced. This is achieved by reducing reflections off the inside surface of the lenses caused by light emanating from a source behind or to the side of the wearer. Anti-reflective coatings can also reduce the effect of ghost images which are caused by duplicate reflections off the inside and outside surfaces of the lenses. In addition, the cosmetic appearance of the eyeglasses is improved by making it possible for the observer to see the eyes of the wearer of the eyeglasses, instead of reflected images from the outer surface of the lenses. Ideally, the ophthalmic lens should be invisible to the observer. Reducing reflection promotes this effect.
The general method followed by a lab for forming optical elements by replication from a mold and cured under an ultraviolet lamp (UV lamp) is well known and fully described in two U.S. Pat. No. 5,110,514, Controlled Casting of a Shrinkable Material, issue date May 5, 1992 and U.S. Pat. No. 5,114,632, Controlled Casting of a Shrinkable Material, issue date May 19, 1992 herein incorporated by reference. Several businesses and individual optometrists have labs on their premises and advertise one hour service for most eyeglasses. Currently, these labs do not have the capability to add optical coatings which must be high vacuum vapor deposited to the lenses after they are made. Therefore, ophthalmic lenses must be shipped to a different facility which can provide such optical coatings, requiring extra expense and up to an additional week in waiting time for the customer. Additionally, high vacuum vapor deposition of coatings coheres to the lenses through physical adhesion and is scratched and/or removed easily with normal use and cleaning.
Another difficulty lies in adding both the competing yet desirable characteristics of a hard coat to the lens for scratch resistance and a tinted coat to absorb transmitted light. After manufacture, a hard coat that can be highly crosslinked is spun onto the outside of a pre-made lens making the outer surface very hard after curing. If the wearer requests tinting, the tintable coating must be spun onto the inside of the pre-made lens because the inside is softer and will absorb the dye. However, because the nature of the adhesion of these coatings is physical, the wearer may damage the coatings through normal use and cleaning.
U.S. Pat. No. 4,061,518, Method for Making an Article Having Replicated Coating with Durable Dielectric Overcoat, issue date Dec. 6, 1977, discloses a method for making an article having a replicated coating with a durable dielectric overcoat. The silicon parting compound, or release layer, is vapor deposited. An optical coating is formed on the coated surface while in the vacuum under a low temperature to cause initial curing of the protective coat without reevaporation of the silicon oil. Thereafter, the optical coating on the master is post-cured in air at an elevated temperature to cause final curing and hardening of the protective coat. After the post-curing has been completed, the replicated part is mounted by a sealing plastic.
U.S. Pat. No. 5,160,668, Method for Forming Optical Elements Having an Optical Coating by Replication of a Mold, issue date Nov. 3, 1992, discloses a method for forming from a mold, optical elements having an optical coating. The method includes high vacuum vapor depositing a release material and an optical coating onto the mold and then adding liquid resin and thermal curing the optical element. High vacuum vapor deposition is expensive. Additionally, even though the optical coating adheres preferentially to the surface of the optical element, the physical adhesion is not strong enough to protect the anti-reflective coat from being scratched and/or removed during normal use and cleaning. Additionally, this disclosure does not solve the problem of the competing characteristics of scratch resistance and tintability.
What is needed is a method and apparatus which will provide on-site formation of completed optical elements having durable optical coatings and a tinted hard coat layer, thereby significantly reducing required handling time and costs.
What is also needed is a method and apparatus for preparing optical elements which permit the transfer of optical coatings and a tinted hard coat layer to the optical element at a different location and time than the deposition of these coatings onto the mold used for forming the optical element.
What is also needed is a method and apparatus which uses a chemical coupler in order to better extract the optical coatings from the mold and to make the optical coatings and optical element more durable than is possible with current technology.